SD can
I have had alot of experience with MP5SD ( factory ) gun through my employer. yes it is very quite if you dont mind the bleed off of the factory HV ammo. I have also used an MP5N with screw on can which does not use a ported barrel to bleed off velocity which, to me is preferable, as to maintain velocity of factory ammo. The MP5SD is made to be used with regular ammo, not subsonic ammo and is not reccomended with heavy (147 or 158) ammo. the SD relies on the bleed off of factory (115 or 124) to obtain subsonic velocities. I have shot many feral hogs with both and the MP5N with screw on can and heavy (147/158gr bullets) is alot more effective. Yes this is just my personal experience. I prefer the MP5N over the SD as I am able to use heavy bullets to achieve subsonic velocities over bleed off of lighter bullets.
Joe